1. Field of the Invention
The present invention relates generally to annular metal-to-metal seals for establishing pressure tight sealing engagement with one or more annular metal components. The present invention is particularly applicable for use when tubular elements are positioned end-to-end in a manner defining a joint therebetween, with the metal-to-metal seal assembly having an elastic component providing a joint seal having a substantially constant radial sealing force. More particularly, the present invention concerns an annular sealing assembly permitting the use of a high strength seal carrier body to which is retained an annular seal insert composed of soft, corrosion resistant metal which is sufficiently deformable by seal activating force of the seal carrier body to conform to the surface geometry and finish of a sealing surface and thus establish an efficient high pressure seal therewith.
2. Description of the Prior Art
A metal-to-metal seal is described as follows in U.S. Pat. No. 4,471,965, commonly assigned herewith: A metal-to-metal sealing system including an annular metallic seal element having a sealing lip with a sealing face of round or curved, as distinguished from annular or flat, cross-sectional configuration, and a cylindrical metallic surface against which the sealing lip presses in a fluid-tight relationship. The cylindrical surface has a lead-in chamber on at least one end to facilitate installation of the seal element into an interference fit against the cylindrical surface, and that surface has sufficient axial length to accommodate relative longitudinal movement between it and the sealing lip as these metallic elements expand and contract in response to changes in temperature. Thus under normal operating conditions such as those existing at times other than during a fire, the seal system functions as a pre-load metal-to-metal seal, and when subjected to a fire or other greatly elevated temperature the interference fit assures that a fluid-tight seal is maintained even though significant longitudinal or radial movement between the sealing lip and the cylindrical surface occurs. Furthermore, during cool down from high temperatures the integrity of the seal remains intact. The result is an effective and reliable metal-to-metal sealing system which provides fluid-tight pressure control over a very wide temperature range, for example for 1200xc2x0 F. to minus 75xc2x0 F., and which can be satisfactorily employed in wellhead equipment as well as other applications where varying temperatures and/or pressures may be encountered.
Current rigid metal sealing technology, such as Straight Bore Metal Seals (SBMS), and FX Bonnet gaskets, and RX, BX and AX gaskets require higher strength alloys to provide structural integrity and sealing force. These types of seals are widely used in gate valve bonnets, surface and subsea connectors, flowbores and generally throughout wellhead equipment. The strength requirements of these alloys can be up to 120,000 psi yield. These seals work by plastically deforming a small area into a smooth opposing surface. The seal contact area is generally small, and these seals are generally (with a few exceptions), not reusable. Often, due to corrosion requirement, high strength nickel alloys are selected for these seals. These seals may be sensitive to surface finish, installation damage and galling.
A primary object of this invention is to provide a high performance and low cost metal-to-metal sealing assembly for use in high pressure seal applications including straight bore metal seal (SBMS) of the nature set forth in U.S. Pat. No. 4,471,965 and further capable of being employed as rough casing metal seals (RCMS), FX bonnet gaskets, RX, BX, AX and other currently used metal-to-metal seal designs.
A novel concept for high-pressure, metal-to-metal sealing which employs a high strength metal seal body or carrier which facilitates application of spring energy or preload force to a soft metal insert carried by the seal body to accomplish high pressure metal-to-metal sealing even under conditions of poor surface finish or irregular sealing surface geometry. The present invention has application to rigid metal-to-metal seal technology including Straight Bore Metal Seals, FX Bonnet Gasket Seals, RX, BX, AX gaskets and others. The present invention represents an improvement to the High Pressure Fire Resistant Seal set forth in U.S. Pat. No. 4,471,965. The concept of the invention involves separating the structural element (body) from the sealing element (soft metal circumferential insert). Seal designs using this technology employ one or more soft metal inserts that are installed by pressing, shrinking or other retention mechanisms on a higher strength seal body or carrier. The higher strength seal body elastically deforms and provides a spring energy characteristic to activate the seal, plastically deforming the soft metal circumferential seal insert when installed. The high strength seal body also confines and protects the soft metal circumferential sealing element against pressure and mechanical abuse. This type of seal increases contact area, allows lower alloy materials (such as 410 stainless steel, 8630, or 4130 steel) to be used for the body of the seal, prevents galling, and also allows the soft metal seal inserts to be replaced, thus enabling reuse of seal bodies. The soft metal circumferential insert will also allow wider machining tolerances, and seal against surfaces that have defects, such as scratches. This seal design may also be tolerant to slightly oval shaped seal bores. The sealing concept of the present invention represents an improvement over metal seals that simply have a soft coating on the surface or require the soft metal to be welded to the high strength component. Coatings have limited wear/corrosion life and cannot fill large defects in the sealing area. Welding the soft metal to the high strength component adds complexity, expense, and limits material selection and may preclude reuse of the seal.
Current high pressure metal sealing technology, such as Straight Bore Metals Seals (SBMS, described in U.S. Pat. No. 4,471,965), Rough Casing Metal Seals, FX Bonnet gaskets, RX, BX and AX seals require higher strength alloys to provide sealing force and structural integrity. These types of seals are widely used in gate valve bonnets, surface and subsea connectors, flow bores and generally throughout a wide range of wellhead equipment for the petroleum industry. The strength requirements of these alloys can be up to 120,000 psi yield. These seals function by plastically deforming a small annular area of a seal element or projection into a smooth opposing annular sealing surface. The seal contact area is generally small, and these seals are generally (with a few exceptions), not reusable. Often, due to corrosion requirements, high strength corrosion resistant alloys (CRAS) are selected for these seals, thus causing the seals to be of considerable expense. Especially if the seals can only be installed once and then discarded, the impact of seals cost is significant. Using higher strength body of a less expensive material, with a soft metal insert made from a more corrosion resistant material, will improve performance and reduce costs in metal-to-metal sealing. In addition to being reusable, the soft metal insert will allow interacting seal components to have wider machining tolerances, enabling sealing against sealing surfaces that have defects, such as scratches or poor finish. Currently technology requires that the sealing surfaces be of 32 microinch RMS quality or better. The soft metal seal inserts of the present invention will function efficiently even when the surface finish of the sealing surfaces is of less than that being typically required at the present time.